I have tried to return MSFS to Vanilla as outlined in the link from TheSevenFlyer as shown reply above. So now I have taken your advice and deleted MSFS through the windows list. It seemed to behave the same as when I deleted it through Steam.
Tomorrow I will try downloading from Steam again. I will try to find the "large Flight Simulator file as well. I know everyone’s system is different but could you tell me the path where you found yours? Or what the file name was.
I agree with you that it is a pain to have to redownload this completely. I have over two years of mods to try and rebuild.
I got my fingers crossed. Hopefully this works!